perfect running 300sd, yet blue coloration around rod bearings - PeachParts Mercedes-Benz Forum

Ted Daniels · #1 03-17-2008, 09:07 PM

just took oil pan off. there's a 'half moon' of blue discoloration on bottom of visible rods. about 1/3 inch wide. engine runs perfect though. quiet almost. no rod noises for sure. How bad is this? Is this perhaps normal when you got so many miles on it?? Is this still a keeper??

oldiesel · #2 03-17-2008, 10:03 PM

Take down a couple of rod caps and see what the bearings and journals look like, if they are smooth and no brass showing on the bearing shells put it back together and drive on.
Don

Ted Daniels · #3 03-17-2008, 10:21 PM

Quote:

Originally Posted by oldiesel

Take down a couple of rod caps and see what the bearings and journals look like, if they are smooth and no brass showing on the bearing shells put it back together and drive on.
Don

that's a good idea. Is that 13mm 12point? I don't have a torque wrench though for when I put them back. I really don't think something's wrong, it's the nicest sounding diesel I ever heard. a little shaking sometimes, but I suspect the rack dampner bolt.
I feel like I shouldn't mess with it. once you mess with something that ain't broken...

#4 03-17-2008, 10:32 PM

Quote:

Originally Posted by Ted Daniels

just took oil pan off. there's a 'half moon' of blue discoloration on bottom of visible rods. about 1/3 inch wide. engine runs perfect though. quiet almost. no rod noises for sure. How bad is this? Is this perhaps normal when you got so many miles on it?? Is this still a keeper??

FWIW, I have rebuilt lots of engines in my years as a mechanic and have seen bluish discoloration more times than I can remember on rod caps. I never really stopped to think about it but my best guess would be it has something to do with the manufacturing process. If the rod had gotten so hot as to discolor the steel....well lets just say it would not be a quiet engine.

t walgamuth · #5 03-17-2008, 11:15 PM

If it has good oil pressure and no rattling of bearings, no way would I take a cap off.

Tom W

Ted Daniels · #6 03-17-2008, 11:40 PM

Quote:

Originally Posted by t walgamuth

If it has good oil pressure and no rattling of bearings, no way would I take a cap off.

Tom W

my thoughts exactly. you touch it you break it

oil pressure very healthy, sounds very quiet in the belly as well. just that color worried me. I've seen it once, on a 350sd that had a broken oil pump (10mm bolts that hold some plate came loose, swirled around in the pan and finally one went through the screen and busted the pump). That made me think...
another thing: there's a rubber end piece that 'covers' the screen. at the oil intake for the pump. that piece broke off, so there's a rubber ring left that still sits at the end of the oil-intake and then there is the rest just sitting in the oilpan. So now I'm worried that that loose rubber piece, which is like 1.5 inch square (but then round) maybe gets sucked onto the screen on a regular basis and then starves the engine of oil

I really though this was a keeper but now I'm sure it'll give me nightmares about swirling rubber debris in oil pans!!
this must have happened to people before?

Hatterasguy · #7 03-18-2008, 01:07 AM

As long as its not knocking and has good oil pressure I wouldn't touch it. Your asking for trouble taking stuff like that apart.

The oil cooler wasn't removed by chance?

617's once in a while seem to put a rod through the block for no reason, I have seen it happen on this site a number of times. And the oil pump chains tend to snap around 300k. other than that the bottom ends never seem to give any trouble.

pawoSD · #8 03-18-2008, 01:40 AM

I inspected my oil pump around 265k when I had my pan off, and the strainer was in perfect shape (had a new one so I replaced it anyways

) but everything looked good, including the oil pump and chain....no visible wear. Should I be worried about sudden destruction as I approach 300k in the next year or two?

Alberta Luthier · #9 03-18-2008, 01:50 AM

Quote:

Originally Posted by pawoSD

I inspected my oil pump around 265k when I had my pan off, and the strainer was in perfect shape (had a new one so I replaced it anyways

) but everything looked good, including the oil pump and chain....no visible wear. Should I be worried about sudden destruction as I approach 300k in the next year or two?

I'm guessing you have measured chain stretch and have a very good idea how worn the chain is...

pawoSD · #10 03-18-2008, 02:32 AM

Quote:

Originally Posted by Alberta Luthier

I'm guessing you have measured chain stretch and have a very good idea how worn the chain is...

I can do that at any time with my X-ray vision.

No...I didn't check it, now I am paranoid again. I'll just have it replaced at 299k.

Ted Daniels · #11 03-18-2008, 11:03 AM

Quote:

Originally Posted by pawoSD

I inspected my oil pump around 265k when I had my pan off, and the strainer was in perfect shape (had a new one so I replaced it anyways

) but everything looked good, including the oil pump and chain....no visible wear. Should I be worried about sudden destruction as I approach 300k in the next year or two?

did yours have some sort of a rubber boot/ adapter attached to the strainer?
I'm looking for a part # to order that 'thing'

P.E.Haiges · #12 03-18-2008, 11:33 AM

Ted,

I replaced that rubber boot a few years ago when the old boot fell off and caused a drop in oil pressure. Keeping the crankcase full of oil kept the oil pressure up OK. I didn't know what caused the drop in oil ressure but I found out when I removed the lower oil pan for another reason and found the boot in the bottom of the pan. Then it was apparent why I had to keep a higher oil levelain the crankcase.

The rubber boot part was readily available from a MB dealer and didn't cost much. Sorry,
I don't remember the P/N and can't find it.

P E H

leathermang · #13 03-18-2008, 07:08 PM

I am with Ted and Tom...
Don't touch it...
It is probably the result of the hardening process... you can see it on brand new bearings most of the time... I have forgotten the name for that type of hardening (reactance?)...... switches the magnetic field back and forth so fast it heats up the metal it is directed to... very nice to make part hard ( and brittle )and keep the other part of the part ductile ( and much less brittle )... this is the same effect needed for swords... and the way it is produced by the Japanese Sword smiths is to paint successively thicker clay in layers towards the back of the sword.. thus the cutting edge is quenched quicker than the thicker part next to it.....

What will be needed when a driveshaft is worked on is the distance from the center of the ujoints to each other....that is what will be asked by a driveshaft rebuilder...

P.E.Haiges · #14 03-18-2008, 07:18 PM

Ted,

Use a dial indicator and see if U can detect any play in the rods bearings. It shouldn't be more than .002 inch.

P E H

Ted Daniels · #15 03-19-2008, 12:17 AM

Quote:

Originally Posted by P.E.Haiges

Ted,

I replaced that rubber boot a few years ago when the old boot fell off and caused a drop in oil pressure. Keeping the crankcase full of oil kept the oil pressure up OK. I didn't know what caused the drop in oil ressure but I found out when I removed the lower oil pan for another reason and found the boot in the bottom of the pan. Then it was apparent why I had to keep a higher oil levelain the crankcase.

The rubber boot part was readily available from a MB dealer and didn't cost much. Sorry,
I don't remember the P/N and can't find it.

P E H

found it. $25 at the dealer.